This invention relates to an apparatus which provides a fork lift material handling capability to a crane. More particularly, this invention relates to a portable, mobile, readily attachable and detachable fork lift attachment for a crane, preferably a hydraulic crane. Still more particularly, this invention relates to a fork lift attachment for a crane which includes means for maintaining the fork lift in a predetermined orientation throughout the entire range of operation of the crane.
The art of material handling has produced a number of material handling devices both for general application, such as a wide variety of types of cranes and ground-based fork lift devices, as well as devices for specialized applications. Such cranes, including hydraulic cranes, have been quite useful in a number of operations for transferring loads from a first location to a second location, particularly where the locations are at substantially different heights. Another of the advantages of cranes is that a crane may be effectively used in an area spaced above the load to be transported so that the floor space, for example, in a warehouse or in a storage area, can be more efficiently utilized.
Another advantage of such cranes in material handling is that the boom on the crane may be telescoped to lift loads from areas near the cab of the crane as well as areas remotely related to the cab. However, cranes have a disadvantage in material handling in that the goods to be removed from storage or placed in storage by the crane generally must be banded together or otherwise wrapped and enveloped with cable or strapping to be secured to the hook of the crane. Such operations are generally time consuming and in the interest of greater efficiency, it would be desirable to be able to transport loads with a crane while avoiding the necessity of banding or cabling the load.
On the other hand, the art has produced a number of land based vehicles which include a fork lift or platform assembly for lifting loads from the ground level to some minimal height relative to the ground, such as on the order of ten to twelve feet. Such fork lift trucks have substantial advantages in rapidly handling loads at the ground level, particularly loads which are palletized. However, a disadvantage of fork lift trucks is that the accessibility of the load is limited to spaces in which the vehicle can maneuver and such devices are not necessarily the most efficient for transporting goods over long distances because of the transit time of the vehicle.
Thus, it is an aim in the art to provide a fork lift attachment for a crane, particularly a hydraulic crane, to provide the same material handling capabilities as a fork lift or stacker truck while retaining the versatility of the crane.
One such device has been disclosed in the patent to Hallsworth, U.S. Pat. No. 3,033,401, issued May 8, 1962 In the device there disclosed, a substantially vertical mast is attached to the boom of a crane member at a point somewhat remote from the end of the boom and a lower point on the mast is secured to a second point on the crane for stability. Such a connection restricts the range of operation of the device. Because of the particular arrangement, the lifting hook for raising the fork lift assembly is disposed above the tines of the fork and thus limits the height of the materials which may be handled. Accordingly, it is an aim in this art to provide a fork lift attachment for use with a crane, which is secured to the crane only at the point of attachment so that the entire arcuate range of the boom of the crane may be used. It is an additional aim in the art in connection with such devices to maintain, insofar as possible, the area above the tines of the fork lift device free from interference to accommodate relatively high loads.
A similar fork lift attachment is disclosed in the U.S. Pat. to McCune, No. 2,941,685, issued June 21, 1960.
Other devices are known to the art which use portable mast assemblies which are intended to be used on a ground surface and in which the lifting member is controlled by the load line of a crane. However, such devices have a distinct lack of the versatility of the portable fork lift attachment of this invention which may be utilized on the extreme end of the boom of a crane and in positions which are free from ground support or other stabilizing connection to the crane.
It has been a substantial problem in the implementation of a device designed to achieve the aims set forth above to provide a mechanism for maintaining the load in a level position or in any other desired orientation, throughout the range of the boom relative to the horizontal, for example, from 0.degree. to 70.degree., or even more. Accordingly, it is a constraint on the development of such devices in order to utilize fully the capabilities of the crane to provide means for leveling the load over the entire range of the crane. For example, the Hallsworth device discloses the use of a limited leveling capability, but such leveling is not available for a very wide range of use for the crane. Still further, it would be desirable in the development of such devices to minimize the number of connections to the crane and the points of attachment. Accordingly, it is an aim of this invention to provide a fork lift attachment for a crane which may be secured near the end of a boom and be utilized free from additional connections to the crane and from ground support so as to be a portable, mobile device and to provide means for leveling the load over the entire range of operation of the boom of the crane.
It is an additional object of this invention to provide a fork lift attachment for a crane in which the elevator lift mechanism is operable utilizing the load line of the crane.
It is an additional object of this invention to provide a portable fork lift attachment for use with the crane which is readily connected and disconnected from the crane so that the crane may be used for other purposes when the fork lift capability is not needed.
It is a further object to this invention to provide a fork lift attachment for a crane which minimizes the mechanical, electrical or hydraulic connections necessary to accommodate the device to the crane.
It is an additional object of this invention to provide means for leveling the load throughout the range of throw of the boom of the crane, and to provide such a leveling capability which may be automatically controlled.
It is an additional object of this invention to provide a device of the type described which may be stored on the ground or other convenient surface and readably attached and detached from the crane.
These and other objects of the invention will become more apparent from the following written description of the invention taken in conjunction with the accompanying drawings.